On Friday, March 18, 2016 at 9:36:51 PM UTC-7, DaleKramer wrote:
On Friday, March 18, 2016 at 11:33:01 PM UTC-4, 2G wrote:
It is high because it IS high. It is 5-6 times higher than an R22.

Ok, so let us concentrate again on the rotor disk loading.
If you had evaluated the design as an engineer, then I would not have to had to assume that you were asking about rotor disk loading versus propeller disk loading. An engineering evaluation would have understood that there are two flight modes that use different disk loading calculations and the question would have been more specific.

Following that, you seem to have categorically determined that it has a very high rotor disk loading without specifying a class. When you start defining the class, you cite vehicles in 2 classes and now finally you are for some reason comparing my design only to a helicopter. It is obviously NOT a helicopter! It is not even in the Osprey tiltrotor class. The closest conventionally categorized class it could be put in is the tiltwing class and in that class it has a low rotor disk loading.

I believe if anyone should be criticized here it is not me.

Somehow we have rubbed each other the wrong way, for that I am sorry.

Dale - It's a pretty clever design. Thanks for sharing - gutsy move.

I expect the main reason to care about disk loading is to work out how many RPM at what propeller lift coefficient you need to produce enough total mass flow to hover. Presumably with the main engine running along with six electric motors you are within the operating parameters of the engines/props you have fitted and the thing can actually hover. It certainly appears to be a more highly loaded hovering design that a traditional single rotor helicopter in the same weight class, but I don't necessarily see that as particularly a big deal for what it's trying to do. I also expect that going to a higher disk loading than a typical conventional single rotor design will have some impact on efficiency and therefore endurance, but since you are not spending much time in vertical mode it's not a big factor for this design.. The bigger considerations here are the overall layout for prop tip clearance and commercially available brushless motor designs and the fact that you need multiple, displaced sources of thrust to control the thing in hover.

I'd have some questions about stability and control in hover mode. First, there is a fair amount of weight above the center of thrust for the electric motors - this includes the pilot and particularly the gas motor which is on a pretty long moment arm. This is a little like balancing a broomstick on the palm of your hand. You will need to counter any static or dynamic pitching moment with differential thrust on the electric motors, which could be problematic particularly in a low-speed transition between hover and forward flight when you have no aerodynamic elevator authority. Presumably the gas motor is pulling pretty hard which is stabilizing as long as you are vertical, but it doesn't provide any restoring pitch moment if you are at some intermediate pitch attitude, but not yet flying like an airplane. You'd need to use differential thrust on the electrics to keep the nose from tipping over, all while providing enough total thrust to hold hover.

A second potential issue is how to counteract the torque of the gas motor and prop, which see to be substantially larger than the electric motors and props. Since hexacopter yaw is controlled by adjusting the speed of the three clockwise turning versus three counter-clockwise turning props you'd have to have enough available angular momentum delta in three electric motors which are not on the centerline to counteract the angular momentum delta of the big gas motor which is on the centerline. I'm not sure how much being off centerline will affect the overall yawing moment.

Ideally, you'd like to be able to handle an electric motor bearing failure at an inopportune time in transition without losing control of the aircraft.. Some model hexacopter controllers deliberately gyrate in yaw to hold attitude with a single engine out. This probably wouldn't be a pleasant experience for a pilot onboard so you might need to consider how (or whether) you want to deal with that scenario.

Glad you're building a model first - lots of interesting challenges to work out.

I wouldn't worry too much about addressing Tom's criticism(s). He is oftentimes challenged understanding or conceding any points not made by him - though it certainly appears in this case that he's mistaken the bottom of the airplane (with the nose wheel stalk) for the top in your drawing of the aircraft with the pilot seat in hover orientation.

Andy